Soulkeep Battle with Slime Trooper and Ivory Tower

I have used Slime Trooper as I have rented it and it is epic tower with a very good stats and I wanted to try it and with Ivory towers which has fire interval of 4 but about 300 magic attack this can hit fiends and eliminate them quickly and I get benefit from Slime Trooper as a strong wall to be able to stop fiends until Ivory Towers attacking them.

In Fact Slime Trooper was a very good spell and one of the best that I have tried as it is a wall and I do not expect spell to be like that, It makes a wall of Slime that stopped fiends from passing and it has a health that is decreasing while fiends trying to pass but it stands all the wave and do not die but I hoped that it can continue even with its health to the second wave but it disappear.

I can use it with 30 Mana and this is not so much for its skills but it has a problem that it is on one way so using it close to gate will be a good solution and I am thinking of putting it just at the gate to close it from fiends but it is itself do not cause damage so needs towers near it.

As for Ivory Tower it is good as it has a good magic attack but with fire interval of 4 it is so hard to eliminate fast fiends with low health but Slime Trooper was a good solution in this situation as it stopped fiends and without this spell Ivory Tower can not be used but still there is a Mana Problem so I need to pass these two waves just to collect mana and then as waves passed I can get more Mana and add more towers and so on.